mTOR inhibition influences cell viability of medullary thyroid carcinoma primary cultures

Effective medical therapy for persistent/recurrent medullary thyroid carcinoma (MTC) is not available, yet. Everolimus (RAD001) is a Rapamycin derivative, a potent mTOR pathway inhibitor. RAD001 has been employed in several clinical studies demonstrating antiproliferative and apoptotic effects in human tumors, both in vitro and in vivo, also in combination with somatostatin analogs. The aim of our study was to investigate the antiproliferative effects of RAD001 in human MTC primary cultures. Of 10 MTC have been dispersed in primary culture and incubated for 24 h in culture medium without serum. Cells have been then treated without or with increasing concentrations of RAD001 (10 nM – 1 μM) and/or 10 nM SOM230 (a multiligand somatostatin analog) and/or 50 nM IGF-1. Cell viability has been evaluated after 24 h with a colorimetric method. Somatostatin receptor (SSTR) expression has been evaluated by quantitative PCR. We found that RAD001 10 nM slightly (−17%) but significantly reduces cell viability in five MTC, and that this effect is blocked by co-treatment with IGF-1. SOM230 alone did not modify cell viability but enhanced the antiproliferative effects of RAD001 (−23%). In this group, SSTR2 was the mostly expressed SSTR subtype (72×103 molecules × μg total RNA), followed by SSTR1 (59×103 molecules × μg total RNA), while SSTR3 and SSTR5 were not expressed. Both RAD001 and SOM230 did not affect cell viability in the other five MTC, which expressed SSTR1, SSTR2, SSTR3 and SSTR5 (33, 32, 35, and 16×103 molecules × μg total RNA). These results indicate that Everolimus might represent a possible medical therapy aimed at controlling MTC cell growth in some cases, in association with somatostatin analogs.